Biology of ischemic and toxic renal tubular cell injury: role of nitric oxide and the inflammatory response

Lipoteichoic acid from Staphylococcus aureus reduces renal ischemia/reperfusion injury

BACKGROUND

The aim of this study was to investigate whether in vivo administration of a low, sub-lethal dose of lipoteichoic acid (LTA), a bacterial wall-fragment derived from the Gram-positive bacterium Staphylococcus aureus, protects the kidney against the renal dysfunction and injury caused by ischemia/reperfusion (I/R).

METHODS

Male Wistar rats were administered LTA from S. aureus (1 mg/kg, IP). After 24 hours, rats were subjected to bilateral renal ischemia (45 min) followed by reperfusion (6 h). Serum and urinary markers were measured for the assessment of renal function, tubular and reperfusion-injury. Renal sections were used for histological grading of renal injury and for immunohistochemical localization of P-selectin, inducible nitric oxide synthase (iNOS) and nitrotyrosine (indicative of peroxynitrite formation). Kidney myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels were measured for assessment of polymorphonuclear (PMN) cell infiltration and lipid peroxidation, respectively. Nitric oxide (NO) production was determined by measurement of plasma nitrite/nitrate levels.

RESULTS

LTA pretreatment significantly reduced renal dysfunction, tubular and reperfusion-injury caused by I/R of the kidney as well as histological evidence of renal injury. LTA also reduced the expression of P-selectin and kidney MPO activity associated with renal I/R. MDA levels were significantly reduced by LTA pretreatment suggesting a reduction in the lipid peroxidation and formation of reactive oxygen species (ROS). LTA pretreatment also markedly reduced both the expression of iNOS and the formation of nitrotyrosine associated with renal I/R. Although LTA significantly reduced plasma nitrite/nitrate levels associated with I/R, nitrite/nitrate levels remained at levels significantly higher than that measured from the plasma obtained from Sham-operated animals.

CONCLUSIONS

These data suggest, to our knowledge for the first time, that LTA pretreatment for 24 hours significantly reduces renal I/R injury. We propose that the mechanism of the protective effect involves reduction of the production of NO, ROS and peroxynitrite subsequent to reduced P-selectin and iNOS expression and PMN recruitment. However, although LTA pretreatment resulted in a reduction of iNOS expression and NO production, we hypothesize that the remaining significant levels of NO contribute to the beneficial actions provided by LTA.

Inhibition of inducible nitric oxide synthase reduces renal ischemia/reperfusion injury

BACKGROUND

Nitric oxide (NO), produced via inducible nitric oxide synthase (iNOS), is implicated in the pathophysiology of renal ischemia/reperfusion (I/R) injury. The aim of this study was to investigate the effects of the iNOS inhibitors L-N6-(1-iminoethyl)lysine (L-NIL) and aminoethyl-isothiourea (AE-ITU) on (a) renal dysfunction and injury mediated by bilateral I/R of rat kidneys in vivo and (b) cytokine-stimulated NO production by primary cultures of rat proximal tubule (PT) cells.

METHODS

Male Wistar rats subjected to bilateral renal ischemia (45 min) followed by reperfusion (6 h). Rats were administered either L-NIL (3 mg/kg IV bolus 15 min prior to I/R followed by 1 mg/kg/h throughout I/R) or AE-ITU (1 mg/kg IV bolus 15 min prior to I/R followed by 1 mg/kg/h throughout I/R). Serum and urinary biochemical indicators of renal dysfunction and injury were measured; serum creatinine (SCr, glomerular dysfunction), fractional excretion of Na+ (FENa, tubular dysfunction), serum aspartate aminotransferase (sAST, I/R injury) and urinary N-acetyl-beta-d-glucosaminidase (uNAG, tubular injury). Additionally, renal sections were used for histological grading of renal injury and for immunological evidence of nitrotyrosine formation. Nitrate/nitrate levels in plasma were measured using the Griess assay and used as an indicator of NO production. Primary cultures of rat PT cells were incubated with interferon-gamma(IFN-gamma, 100 IU/mL) and lipopolysaccharide (LPS, 10 microg/mL) for 24 h, either in the absence or presence of increasing concentrations of L-NIL or AE-ITU (0.001 to 1 mmol/L) after which nitrite/nitrate levels were measured using the Griess assay.

RESULTS

L-NIL and AE-ITU significantly reduced the I/R-mediated increases in SCr, FENa, sAST and uNAG, indicating attenuation of I/R-mediated renal dysfunction and injury. Specifically, L-NIL and AE-ITU reduced the I/R-mediated glomerular and tubular dysfunction and biochemical and histological evidence of tubular injury. Both L-NIL and AE-ITU attenuated the plasma levels of nitrate (indicating reduced NO production) and the immunohistochemical evidence of the formation of nitrotyrosine. In vitro, L-NIL and AE-ITU both significantly reduced cytokine-stimulated NO production by primary cultures of rat PT cells in a dose-dependent manner.

CONCLUSIONS

These results suggest that L-NIL and AE-ITU reduce the renal dysfunction and injury associated with I/R of the kidney, via inhibition of iNOS activity and subsequent reduction of NO (and peroxynitrite) generation. We propose that selective and specific inhibitors of iNOS activity may be useful against the NO-mediated renal dysfunction and injury associated with I/R of the kidney.

Protective role of nitric oxide in a model of thrombotic microangiopathy in rats

Anew model of thrombotic microangiopathy (TMA) was previously developed, and it was demonstrated that endothelial nitric oxide (NO) synthase (NOS) is upregulated in glomeruli in this model. It was hypothesized that the synthesis of NO, a potent vasodilator and platelet inhibitory factor, is induced as a defense mechanism. The goal of this study was to clarify the role of NO in this model. Ex vivo experiments using Western blotting and functional assays demonstrated upregulation of endothelial NOS in isolated glomeruli from TMA rats. In in vivo experiments, five groups of rats were studied, including rats with TMA treated with vehicle, N(G)-nitro-L-arginine methyl ester (L-NAME) (a NOS inhibitor), or L-N(6)-(1-iminoethyl)lysine (L-NIL) (a specific inducible NOS inhibitor) and normal control rats treated with vehicle or L-NAME. Blood urea nitrogen levels, BP, urinary nitrate/nitrite excretion, and proteinuria were measured. Histologic assessments using periodic acid-Schiff staining and immunohistologic studies with markers for endothelium, platelets, fibrin, cell proliferation, and apoptosis were also performed. L-NAME inhibition of NO synthesis in rats with TMA resulted in more severe glomerular and tubulointerstitial injury, which was accompanied by thrombus formation and a marked loss of endothelial cells, with more apoptotic cells. These changes were associated with severe renal function deterioration. In contrast, these features were less pronounced in the vehicle- or L-NIL-treated rats with TMA and were absent in the control animals. In conclusion, inhibition of NO production in this model of TMA markedly exacerbated renal injury. The absence of effects with L-NIL treatment suggests a minor role for inducible NOS in this model. These results suggest that production of NO, most likely by endothelial cells, is an important protective mechanism in TMA.

Effect of mycophenolate mofetil on nitric oxide production and inducible nitric oxide synthase gene expression during renal ischaemia-reperfusion injury

BACKGROUND

Recent animal data suggest that inducible nitric oxide synthase (iNOS) derived nitric oxide (NO) plays an important role in the pathogenesis of renal ischaemia-reperfusion injury (IRI) and that inhibition of iNOS ameliorates IRI. Mycophenolate mofetil (MMF), a lymphocyte selective anti-proliferative agent, has been shown to inhibit NO production in vitro. The aim of this study is to evaluate the effect of MMF on NO production and iNOS gene expression in vivo during renal IRI.

METHODS

Renal IRI was induced by clamping the left renal pedicle of male BALB/c mice for 30 min, followed by 15 min of reperfusion. The mice received placebo or MMF at 40, 80 or 120 mg/kg/day by oral gavage for 5 days before the operation. Sham-operated mice served as the operation control. The amount of NO produced and the level of iNOS gene expression in the kidney tissue during IRI was assessed by spin trapping electron paramagnetic resonance (EPR) spectroscopy and semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) respectively.

RESULTS

In the sham-operated kidneys, only low levels of NO and iNOS mRNA were detected. In mice with renal IRI, the amount of NO detected was significantly increased, which was reduced in a dose dependent fashion by pre-treatment with MMF. Pre-treatment with MMF also substantially reduced iNOS gene expression in the kidney tissue.

CONCLUSIONS

We conclude that pre-treatment with MMF inhibits the production of NO and the induction of iNOS gene expression in the kidney during IRI. These results suggest that MMF might have the potential to ameliorate renal IRI.

Identification and kinetics of leukocytes after severe ischaemia/reperfusion renal injury

BACKGROUND

Leukocyte adhesion/infiltration in response to renal ischaemia/reperfusion (I/R) injury is a well-known but poorly understood phenomenon. The identification, kinetics, and exact role of these inflammatory cells in I/R injury and regeneration are still matters of debate.

METHODS

Uninephrectomized rats were submitted to 60 min renal ischaemia by clamping of renal vessels.

RESULTS

Severe acute renal failure was observed, with maximum functional impairment on day 2. By 12 h after the ischaemic event, up to 80% of proximal tubular cells in the outer stripe of outer medulla (OSOM) were already severely damaged. Proliferation (proliferating cell nuclear antigen (PCNA) staining) started after 24 h, reaching maximum activity on day 3. Regeneration of tubular morphology started on the 3rd day, and after 10 days 50% of tubules had regenerated completely. Interstitial leukocytes (OX-1 immunohistochemical staining) were already prominent at day 1, thereafter gradually increasing with time. The so-called neutrophil-specific identification methods (myeloperoxidase (MPO), chloroacetate esterase, mAb HIS-48) proved to be non-specific, since they also stained for macrophages, as demonstrated by flow cytometry and the combination of these stainings with the macrophage-specific ED-1 staining. MPO activity was already significantly increased at 1 h post-I/R (439+/-34%, P<0.005), reaching its maximum activity after 12 h of I/R (1159+/-138%, P<0.0005), declining thereafter. On the other hand, neutrophil presence investigated by H&E staining revealed only a few neutrophils in glomeruli, medullary rays, and OSOM at 24 h after the ischaemic event (4.7+/-4.2 cells/mm(2) vs controls=2.3+/-2.0 cells/mm(2) (n.s.)), and remained unchanged over the next 10 days. In contrast, significant monocyte/macrophage adhesion/infiltration (ED-1 staining) occurred at the OSOM at 24 h post-ischaemia (at 24 h, 120+/-46 cells/mm(2) vs. sham=18+/-4 cells/mm(2) (P<0.05)), became prominent at day 5 (1034+/-161 cells/mm(2) vs sham=18+/-18 cells/mm(2) (P<0.05)), and almost disappeared after 10 days. CD4(+) cells (W3/25) gradually increased from day 5, reaching a maximum at day 10. A few CD8(+) cells (OX-8) were apparent from days 3 until 10, but no B-cells (OX-33) were observed.

CONCLUSIONS

After severe warm I/R renal injury, a pronounced acute tubular necrosis occurs during the first 12-24 h in the absence of a marked cellular infiltrate, but with an important renal MPO activity, reflecting the activation of the adhering inflammatory cells (polymorphonuclear cells (PMNs) and mainly monocytes/macrophages). Only later at the time and site (OSOM) of regeneration a sequential accumulation of monocytes/macrophages and T cells becomes prominent, in contrast with the low number of neutrophils found in the kidney during the 10-day post-ischaemic period. The non-specificity of the so-called neutrophil-specific identification methods (MPO activity, naphthol AS-D chloroacetate esterase, or mAb HIS-48 staining), cross-reacting with monocytes/macrophages, explains the controversy in literature concerning the number of PMNs in post-ischaemic injury.

Up-regulation of galectin-3 in acute renal failure of the rat

Galectin-3, a multifunctional beta-galactoside-binding lectin, is known to participate in development, oncogenesis, cell-to-cell attachment, and inflammation. We studied to determine whether galectin-3 is associated with cell injury and regeneration in two types of acute renal failure (ARF), namely ischemic and toxic ARF. In ischemia/reperfusion renal injury in rats (bilateral renal pedicles clamped for 40 minutes), galectin-3 mRNA began to increase at 2 hours and extended by 6.2-fold at 48 hours (P: < 0.01 versus normal control rats), and then decreased by 28 days after injury. In addition, a significant negative correlation between galectin-3 mRNA expression and serum reciprocal creatinine was shown at 48 hours after injury (n = 13, r = -0.94, P: < 0.0001). In folic acid-induced ARF, galectin-3 mRNA was found to be up-regulated at 2 hours after injury and increased levels continued until at least 7 days post-injury. In immunohistochemistry, at 2 hours following reperfusion, galectin-3 began to develop in proximal convoluted tubules. From 6 hours up to 48 hours, galectin-3 was also found in proximal straight tubules, distal tubules, thick ascending limbs, and collecting ducts. In later stages of regeneration, galectin-3 expressions were found in macrophages. In conclusion, we demonstrated that galectin-3 expressions were markedly up-regulated in both ischemic and toxic types of ARF. Galectin-3 may play an important role in acute tubular injury and the following regeneration stage.

Antibodies to both ICAM-1 and LFA-1 do not protect the kidney against toxic (HgCl2) injury

BACKGROUND

The role of inflammatory leukocytes in acute renal failure (ARF) remains controversial and appears largely uninvestigated in toxic (in contrast to ischemic) ARF.

METHODS

Female Wistar rats were injected with monoclonal antibodies (mAbs) directed to both the leukocyte function-associated antigen 1 (LFA-1) and the intercellular adhesion molecule 1 (ICAM-1). Doses (6 mg/kg of each mAb) were given 24 hours prior to the induction of acute tubular necrosis (ATN) by mercuric chloride administration (2 mg/kg, subcutaneously, day 0) and subsequently every 48 hours. Control rats similarly received either control antibody (12 mg/kg) or vehicle prior to and following the induction of ATN. Renal function was also measured from male Lewis rats that were similarly treated with anti-adhesion antibodies during exposure to 30 minutes of unilateral renal ischemia.

RESULTS

Injected antibodies were demonstrated on peripheral blood leukocytes (flow cytometrical detection of mouse anti-LFA-1) and on endothelium (immunohistochemical staining of mouse anti-ICAM-1) and were measured in serum (enzyme-linked immunosorbent assay). Macrophages and T cells were prominent in the kidney of control treatment rats after HgCl2 injection, but anti-adhesion treatment clearly had prevented their infiltration. Notwithstanding, renal tubular injury was equally pronounced in all mercuric chloride treatment groups and so was the decline in renal function (serum creatinine, proteinuria). Tubular epithelial cell proliferation seemed slightly less pronounced and delayed in anti-adhesion treated rats. Kidneys from ischemia exposed rats were, however, functionally protected by identical anti-ICAM-1/anti-LFA-1 treatment.

CONCLUSION

Prevention of cellular infiltration by mAbs to LFA-1 and ICAM-1 has no effect on renal morphology, function, or regeneration following mercuric chloride-induced ARF in the rat. This result contrasts with the functional protection of the rat kidney to ischemia/reperfusion injury by virtue of an identical antibody treatment protocol. Resolving that controversy should bring better insight in fundamental processes underlying different types of ARF, and will be the subject of further study.

Acute renal failure. III. The role of growth factors in the process of renal regeneration and repair

This review, which is the final installment in a series devoted to controversial issues in acute renal failure (ARF) (3, 47), will examine available information regarding the role of growth factors in ARF. In general, studies in this area have fallen into two broad categories: 1) those that have examined the renal expression of genes encoding growth factors or transcriptional factors associated with the growth response that is induced after ARF, and 2) those that have examined the efficacy of exogenously administered growth factors in accelerating recovery of renal function in experimental models of ARF. Despite the vast amount of information that has accumulated in these two areas of investigation, our understanding of the mechanisms involved in the process of regeneration and repair after ARF, and the role of growth factors in this response, remains rudimentary. This overview, contributed to by a number of experts in the field, is designed to summarize present knowledge and to highlight potentially fertile areas for future research in this area.

Chronic reduction in renal mass in the rat attenuates ischemia/reperfusion injury and does not impair tubular regeneration

It is not known whether a kidney with chronic structural and functional changes is more vulnerable to an acute renal insult, and whether its regeneration capacity after injury is altered. To study this question, Lewis rats were submitted 10 wk after 5/6 nephrectomy to an ischemic insult of 60 min (remnant kidney [RK] group). Functional and morphologic data of the RK group were compared with data obtained in 10-wk uninephrectomized (1K) and normal (2K) Lewis rats with unilateral and bilateral renal ischemia, respectively. The acute postischemic decrease in creatinine clearance was smallest in the RK group, followed by the 2K and 1K groups, respectively. At days 1 and 3, fewer proximal tubules in the outer stripe of the outer medulla of the RK and 2K groups had undergone acute tubular necrosis compared with the 1K group. The mean percentage of tubules with signs of regeneration was maximal at day 3 in the three experimental groups. At day 10, regeneration was almost complete in the three groups. The number of leukocytes (OX1+ cells) present in the RK before ischemia did not increase after ischemia/reperfusion injury (377 +/- 146 cells/mm2 at day 0) in contrast to the 1K and 2K groups. In the latter groups, the number of leukocytes had increased gradually, reaching a maximum at day 15 (1K: 960 +/- 308 cells/mm2) and day 10 (2K: 668 +/- 164 cells/mm2), respectively. In conclusion, this study has shown that an RK exhibiting chronic morphologic changes of interstitial fibrosis and tubular atrophy is protected against ischemia/reperfusion injury, and that its regeneration capacity is preserved. The reperfusion injury is not followed by further accumulation of leukocytes, which were already present in the RK before ischemia.

ATP depletion increases tyrosine phosphorylation of beta-catenin and plakoglobin in renal tubular cells

This study examines the hypothesis that the loss of integrity of the junctional complex induced by ATP depletion is related to alterations in tyrosine phosphorylation of the adherens junction proteins beta-catenin and plakoglobin. ATP depletion of cultured mouse proximal tubular (MPT) cells induces a marked increase in tyrosine phosphorylation of both beta-catenin and plakoglobin. The tyrosine phosphatase inhibitor vanadate has the same effect in ATP-replete (control) monolayers, whereas genistein, a tyrosine kinase inhibitor, reduces phosphorylation of both proteins in ATP-replete monolayers and prevents the hyperphosphorylation of these proteins with ATP depletion. This study also demonstrates that the fall in the transepithelial resistance of MPT monolayers induced by ATP depletion can be reproduced by treatment of ATP-replete monolayers with vanadate, whereas genistein substantially ameliorates the fall in transepithelial resistance induced by ATP depletion. Also, using immunofluorescence microscopy it was demonstrated that ATP depletion results in a marked diminution of E-cadherin staining in the basolateral membrane of MPT cells. Vanadate mimics this effect of ATP depletion, whereas genistein ameliorates the reduction in the intensity of E-cadherin staining induced by ATP depletion. Because it is has been well established that hyperphosphorylation of the catenins leads to dissociation of the adherens junction and to dysfunction of the junctional complex, it is proposed that the increase in tyrosine phosphorylation of catenins observed in MPT cells during ATP depletion contributes to the loss of function of the junctional complex associated with sublethal injury.

Nitrite reductase activity is a novel function of mammalian mitochondria

Nitrite, which is the major stable degradation product of nitric oxide, exists in all tissues capable of nitric oxide synthesis from L-arginine. The present study provides experimental evidence that nitrite in contact with respiring mitochondria accepts reducing equivalents from the ubiquinone cycle of the respiratory chain. Univalent reduction of nitrite was totally inhibited by myxothiazol. We therefore conclude on the involvement of redox cycling that ubisemiquinone is associated with the bc1 complex. Recycling of nitric oxide degradation products via these electron carriers may become a threat to energy-linked respiration since nitric oxide in direct contact with mitochondria was shown to slow the energy-linked respiration down and to trigger a mitochondrial source for superoxide radicals. Until now, the existence of nitrite reductase activity was only demonstrated in plants and bacteria. In addition, the present observation elucidates the existence of a nitric oxide synthase-independent nitric oxide source.